Mechanism to provide test access to third-party macro circuits embedded in an ASIC (application-specific integrated circuit)

ABSTRACT

Novel structures and testing methods for the FPGAs (Field-Programmable Gate Arrays) embedded in an ASIC (Application-Specific Integrated Circuits). Basically, a shift/interface system is coupled between the FPGAs and the ASIC. During normal operation, the shift/interface system electrically couples the FPGAs to the ASIC. During the testing of the FPGAs, the shift/interface system scans in FPGA test data in series, then feeds the FPGA test data to the FPGAs, then receives FPGA response data from the FPGAs, and then scans out the FPGA response data in series. During the testing of the ASIC, the shift/interface system scans in ASIC test data in series, then feeds the ASIC test data to the ASIC, then receives ASIC response data from the ASIC, and then scans out the ASIC response data in series.

This application is a Divisional of Ser. No. 10/906,467, filed Feb. 22, 2005, now U.S. Pat. No. 7,308,630.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to FPGAs (Field-Programmable Gate Arrays), and more particularly, to testing of FPGAs embedded in an ASIC (Application-Specific Integrated Circuits).

2. Related Art

An FPGA (Field-Programmable Gate Array) and an ASIC (Application-Specific Integrated Circuit) can be combined to form a hybrid IC (integrated circuit) so that the hybrid IC can have the advantages of both the FPGA (design flexibility) and the ASIC (low power, high performance, and low test pin count).

Testing a standalone FPGA typically consists of exhaustively testing the logic blocks and interconnect resources of the FPGA through a series of structural tests. These structural tests configure the standalone FPGA in different ways and require access to all input/output (I/O) pins of the standalone FPGA. Similarly, testing the FPGA in the hybrid IC consists of essentially the same structural tests. The problem is how to access all I/O pins of the FPGA in the hybrid IC given the low test pin count of the hybrid IC.

Therefore, there is a need for a novel structure and testing method for a low test pin count, hybrid IC comprising an ASIC and multiple FPGAs.

SUMMARY OF THE INVENTION

The present invention provides a digital system, comprising (a) N macro circuits, N being a positive integer; (b) an application-specific integrated circuit (ASIC); and (c) a shift/interface system being coupled to the N macro circuits and the ASIC, wherein, in response to the N macro circuits and the ASIC being in normal operation, the shift/interface system electrically couples each macro circuit of the N macro circuits to the ASIC, wherein, in response to the N macro circuits being tested, the shift/interface system is further configured to scan-in macro circuit test data in series, then to feed the macro circuit test data to the N macro circuits, then to receive macro circuit response data from the N macro circuits, and then to scan-out the macro circuit response data in series, and wherein, in response to the ASIC being tested, the shift/interface system is further configured to scan-in ASIC test data in series, then to feed the ASIC test data to the ASIC, then to receive ASIC response data from the ASIC, and then to scan-out the ASIC response data in series.

The present invention also provides a system testing and operating method, comprising the steps of (a) providing a digital system including (i) N macro circuits, (ii) an application-specific integrated circuit (ASIC), and (iii) a shift/interface system being coupled to the N macro circuits and the ASIC; (b) in response to the N macro circuits and the ASIC being in normal operation, using the shift/interface system to electrically couple each macro circuit of the N macro circuits to the ASIC; (c) in response to the N macro circuits being tested, (i) scanning-in macro circuit test data in series into the shift/interface system, (ii) feeding the macro circuit test data from the shift/interface system to the N macro circuits, (iii) using the shift/interface system to receive macro circuit response data from the N macro circuits, and (iv) scanning-out the macro circuit response data in series from the shift/interface system; and (d) in response to the ASIC being tested, (i) scanning-in ASIC test data in series into the shift/interface system, (ii) feeding the ASIC test data from the shift/interface system to the ASIC, (iii) using the shift/interface system to receive ASIC response data from the ASIC, and (iv) scanning-out the ASIC response data in series from the shift/interface system.

The present invention also provides a system testing method, comprising the steps of (a) providing a digital system including (i) a macro circuit, (ii) an application-specific integrated circuit (ASIC), and (iii) a shift/interface system being coupled to the macro circuit and the ASIC, and (iv) a multiple-input signature register (MISR) including K MISR stages, K being a positive integer, the K MISR stages being coupled together, being coupled to K output pins of the macro circuit, and being coupled to K shift/interface circuits of the shift/interface system, wherein the K shift/interface circuits are coupled together; (b) scanning-in macro circuit test data in series into the shift/interface system; (c) transmitting the macro circuit test data from the shift/interface system to the macro circuit in parallel; (d) using the macro circuit to process the macro circuit test data into macro circuit response data and to present the macro circuit response data at the K output pins of the macro circuit; (e) transmitting the macro circuit response data from the K output pins of the macro circuit to the K MISR stages; (f) using the MISR to process the macro circuit response data into a macro circuit response signature and send the macro circuit response signature to the K shift/interface circuits; and (g) scanning the macro circuit response signature out of the K shift/interface circuits in series.

The present invention provides a novel structure and testing method for a low test pin count, hybrid IC comprising an ASIC and multiple FPGAs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a testing system comprising an IC (integrated circuit) and a tester, the IC comprising a shift/interface system, in accordance with embodiments of the present invention.

FIG. 1B illustrates a method for operating the testing system of FIG. 1A.

FIGS. 2A-2E illustrate embodiments of shift/interface circuits of the shift/interface system of FIG. 1A, in accordance with embodiments of the present invention.

FIG. 3 illustrates one embodiment of a shift/store unit that can be used in the shift/interface circuits of FIGS. 2A-2E, in accordance with embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A illustrates a testing system 100 comprising an IC (integrated circuit) 110 and a tester 120, in accordance with embodiments of the present invention. In one embodiment, illustratively, the IC 110 can comprise FPGAs (Field-Programmable Gate Arrays) 130 a and 130 b, MISRs (Multiple-Input Signature Registers) 140 a and 140 b, a shift/interface system 150, and an ASIC (Application-Specific Integrated Circuit) 160. In general, the IC 110 can comprise M FPGAs similar to the FPGAs 130 a and 130 b, and M MISRs similar to the MISRs 140 a and 140 b (M is positive integer).

The FPGA 130 a is coupled to the shift/interface system 150 via connections 133 a and to the MISR 140 a via connections 135 a. The MISR 140 a is coupled to the shift/interface system 150 via connections 145 a. Similarly, the FPGA 130 b is coupled to the shift/interface system 150 via connections 133 b and to the MISR 140 b via connections 135 b. The MISR 140 b is coupled to the shift/interface system 150 via connections 145 b. The shift/interface system 150 is coupled to the ASIC 160 via connections 155 and to the tester 120 via connections 157. The ASIC 160 is coupled to the tester 120 via connections 165.

In one embodiment, during the normal operation of the IC 110 (i.e., the ASIC 150 and the FPGAs 130 a and 130 b are in normal operation), the shift/interface system 150 can be configured to (a) electrically couple the FPGAs 130 a to the ASIC 150 via the connections 133 a and 155 and (b) electrically couple the FPGAs 130 b to the ASIC 150 via the connections 133 b and 155. In other words, during the normal operation of the IC 110, the shift/interface system 150 is transparent to the FPGAs 130 a and 130 b and the ASIC 150.

In one embodiment, a structural test 180 (FIG. 1B) of the FPGAs 130 a and 130 b can be carried out as follows. With reference to FIGS. 1A and 1B, illustratively, in step 182, the tester 120 can place the FPGAs 130 a and 130 b in a safe (i.e., shut-off) state by sending a stability signal to both the FPGAs 130 a and 130 b. As a result, random signals on the inputs (not shown) of the FPGAs 130 a and 130 b would not place the FPGAs 130 a and 130 b into an unknown or unstable state. In one embodiment, the tester 120 can send the stability signal to both the FPGAs 130 a and 130 b through the connections 157, the shift/interface system 150, and then the connections 133 a and 133 b, respectively.

Next, in step 184, with the FPGAs 130 a and 130 b being placed in the safe state, in one embodiment, the tester 120 can make a first data shift of a first bitstream comprising first FPGA test data and second FPGA test data into the shift/interface system 150 via connection 157. The first data shift is carried out such that, at the end of the first data shift, the first FPGA test data is applied to the input pins of the FPGA 130 a via the connections 133 a, and the second FPGA test data is applied to the input pins of the FPGA 130 b via the connections 133 b.

Next, in step 186, in one embodiment, the tester 120 can send an operation signal to the FPGAs 130 a and 130 b so as to place the FPGAs 130 a and 130 b in an operation state. In one embodiment, the tester 120 can send the operation signal to the FPGAs 130 a and 130 b by deactivating the stability signal.

Next, in step 188, in one embodiment, the tester 120 can send configuration signals to the FPGAs 130 a and 130 b so as to configure the FPGAs 130 a and 130 b to operate on the first and second FPGA test data, respectively. In one embodiment, the tester 120 can send the configuration signals to the FPGAs 130 a and 130 b through the connections 157, the shift/interface system 150, and then the connections 133 a and 133 b, respectively.

Next, in step 190, in one embodiment, the FPGA 130 a can send a first reset signal to the MISR 140 a via the connections 135 a so as to reset the MISR 140 a. In one embodiment, the FPGA 130 b can send a second reset signal to the MISR 140 b via the connections 135 b so as to reset the MISR 140 b.

Next, in step 192, in one embodiment, the FPGAs 130 a and 130 b and the MISRs 140 a and 140 b are clocked N times (N can be selected based on the design of the FPGAs 130 a and 130 b). In one embodiment, the FPGAs 130 a and 130 b and the MISRs 140 a and 140 b can be clocked by a same clock signal.

In one embodiment, for each of the N clocks, the FPGA 130 a generates a different FPGA response to both the MISR 140 a (via connections 135 a) and the shift/interface system 150 (via connections 133 a). At the shift/interface system 150, the current FPGA response overrides and replaces the previous FPGA response. But, at the MISR 140 a, the current FPGA response is combined with all previous FPGA responses from the FPGA 130 a such that after the N clocks, the MISR 140 a combines all the N FPGA responses from the FPGA 130 a into a first response signature. In one embodiment, after the N clocks, the FPGA 130 a can also send its configuration status from its configuration status outputs to the shift/interface system 150 via connections 133 a.

Similarly, for each of the N clocks, the FPGA 130 b generates a different FPGA response to both the MISR 140 b (via connections 135 b) and the shift/interface system 150 (via connections 133 b). At the shift/interface system 150, the current FPGA response overrides and replaces the previous FPGA response. But, at the MISR 140 b, the current FPGA response is combined with all previous responses such that after the N clocks, the MISR 140 b combines all the N responses from the FPGA 130 b into a second response signature. In one embodiment, after the N clocks, the FPGA 130 b can also send its configuration status from its configuration status outputs to the shift/interface system 150 via connections 133 b.

Next, in step 194, in one embodiment, the tester 120 can send the stability signal to both the FPGAs 130 a and 130 b to place the FPGAs 130 a and 130 b in the safe state.

Next, in step 196, in one embodiment, the shift/interface system 150 can make a second data shift of a second bitstream comprising the first and second response signatures and the configuration status of the FPGA 130 a and 130 b out of the shift/interface system 150 to the tester 120 via connections 157.

Next, in one embodiment, one or more structural test of the FPGAs 130 a and 130 b similar to the structural test 180 described supra can be performed.

FIGS. 2A-2E, respectively, illustrate five shift/interface circuits 151 a, 151 b, 151 c, 151 d, and 151 e representative of five different types of shift/interface circuits of the shift/interface system 150 of FIG. 1A (hereafter also referred to as types 151 a, 151 b, 151 c, 151 d, and 151 e), in accordance with embodiments of the present invention. Hereafter, a shift/interface circuit of any of the five types above can be referred to as the shift/interface circuit 151.

In one embodiment, the shift/interface system 150 of FIG. 1A can comprise one chain of multiple shift/interface circuits 151 each of which can be of any one of the five types 151 a, 151 b, 151 c, 151 d, and 151 e (FIGS. 2A, 2B, 2C, 2D, and 2E, respectively). For example, one shift/interface circuit 151 in the chain can be of type 151 a (FIG. 2A), while the next shift/interface circuit 151 in the chain can be of type 151 c (FIG. 2C).

In one embodiment, the chain can have none, one, or more shift/interface circuits 151 of each type of the five types 151 a, 151 b, 151 c, 151 d, and 151 e (FIGS. 2A, 2B, 2C, 2D, and 2E, respectively).

In one embodiment, the shift/interface circuits 151 of a same type are arranged electrically next to each other in the chain. For example, all shift/interface circuits 151 of type 151 a (FIG. 2A) of the chain can be placed electrically next to each other in the chain (two shift/interface circuits 151 are electrically next to each other in the chain if an output of one of the two shift/interface circuits 151 is electrically and directly coupled to an input of the other).

In one embodiment, each shift/interface circuits 151 in the chain, regardless of type, comprises a shift/store unit 210 and a multiplexer (i.e., MUX) 220 (FIGS. 2A-2E). In one embodiment, the shift/store unit 210 can function as a one-bit shift register. That is, in a store mode, the shift/store unit 210 can store a bit applied to its DI input and place the bit on its SO output. In a shift mode, for each shift, the shift/store unit 210 can shift its stored bit at its SO output to the next shift/store unit and receive a bit through its SI input from the immediately preceding shift/store unit.

In one embodiment, the SI input of the shift/store unit 210 of each shift/interface circuit 151 in the chain is electrically and directly coupled to the SO output of the shift/store unit 210 of the previous shift/interface circuit 151 in the chain. Exception is for the first shift/interface circuit 151 in the chain whose SI input (i.e., the SI input of its shift/store unit 210) is electrically coupled to the tester 120 via connections 157. Exception is also for the last shift/interface circuit 151 in the chain whose SO output (i.e., the SO output of its shift/store unit 210) is also electrically coupled to the tester 120 via connections 157.

The following discussion will show how each type of the five types 151 a, 151 b, 151 c, 151 d, and 151 e (FIGS. 2A, 2B, 2C, 2D, and 2E, respectively) helps in the structural test 180 (FIG. 1B).

FIG. 2A illustrates the shift/interface circuit 151 a (i.e., a shift/interface circuit 151 of type 151 a) that can be used in the shift/interface system 150 of FIG. 1A, in accordance with embodiments of the present invention. With reference to FIGS. 1A and 2A, for type 151 a, in one embodiment, the MUX 220 can have its first and second inputs electrically coupled to an output of the ASIC 160 (via connection 155 a, a part of connections 155 FIG. 1A) and the SO output of the shift/store unit 210, respectively. The MUX 220 can have its output electrically coupled to an input of the FPGA 130 a (via connection 136 a, a part of connections 133 a of FIG. 1A) and to the DI input of the shift/store unit 210. The MUX 220 can have its control input receiving a Test-FPGA signal from the tester 120 via connection 157 a, a part of connections 157 of FIG. 1A. In short, the output of the ASIC 160 is coupled to the input of the FPGA 130 a via the shift/interface circuit 151 of type 151 a.

In one embodiment, assume that the FPGA 130 a has P functional data inputs that need to be directly coupled one-to-one to P functional data outputs of the ASIC 160 during the normal operation of the IC 110 of FIG. 1A (P is a positive integer). As a result, P shift/interface circuits 151 of type 151 a can be used in the chain to couple the P functional data outputs of the ASIC 160 to the P functional data inputs of the FPGA 130 a.

During the normal operation of the IC 110, with reference to FIGS. 1A and 2A, the tester 120 can pull the Test-FPGA signal low (i.e., 0) to cause the P MUXes 220 of the P shift/interface circuits 151 of type 151 a to electrically couple the P functional data outputs of the ASIC 160 to the P functional data inputs of the FPGA 130 a. In other words, during the normal operation of the IC 110, the shift/interface system 150 is transparent to the FPGA 130 a and the ASIC 160 as far as the functional data is concerned.

During the structural test 180 (FIG. IB) of the FPGA 130 a, in step 184, in one embodiment, after the first data shift, the P shift/store units 210 of the P shift/interface circuits 151 of type 151 a of the chain should contain the first FPGA test data. Then, with the Test-FPGA signal pulled high by the tester 120, the P MUXes 220 of the P shift/interface circuits 151 of type 151 a apply the first FPGA test data (at the P SO outputs of the P shift/store units 210) to the P functional data inputs of the FPGA 130 a which disconnects the P functional data inputs of the FPGA 130 a from the ASIC 160 during application by the MUXes 220 of the first FPGA test data to the P functional data inputs of the FPGA 130 a.

During the testing of the ASIC 160, the tester 120 can pull the Test-FPGA signal low (i.e., 0) to electrically couple the P outputs of the ASIC 160 to the P DI inputs of the P shift/interface circuits 151 of type 151 a. As a result, signals on the P outputs of the ASIC 160 can be stored in the P shift/interface circuits 151 of type 151 a and can be later shifted out to the tester 120 for analysis.

In one embodiment, multiple shift/interface circuits 151 of type 151 a can also be used to couple functional data outputs of the ASIC 160 to functional data inputs of the FPGA 130 b in a manner similar to that for the FPGA 130 a. In one embodiment, the testing of the FPGAs 130 a and 130 b can be carried out simultaneously in a similar manner.

FIG. 2B illustrates the shift/interface circuit 151 b (i.e., a shift/interface circuit 151 of type 151 b) that can be used in the shift/interface system 150 of FIG. 1A, in accordance with embodiments of the present invention. With reference to FIGS. 1A and 2B, for type 151 b, in one embodiment, the MUX 220 can have its first and second inputs electrically coupled to an output of the ASIC 160 (via connection 155 b, a part of connections 155 of FIG. 1A) and an output of the tester 120, respectively. The MUX 220 can have its output electrically coupled to the input DI of the shift/store unit 210 and an input of the FPGA 130 a via connection 136 b, a part of connections 133 a of FIG. 1A. The MUX 220 can have its control input receiving the Test-FPGA signal from the tester 120. In short, the output of the ASIC 160 is coupled to the input of the FPGA 130 a via the shift/interface circuit 151 of type 151 b.

In one embodiment, assume that the FPGA 130 a has Q configuration inputs that need to be directly coupled one-to-one to Q configuration outputs of the ASIC 160 during the normal operation of the IC 110 of FIG. 1A (Q is a positive integer). As a result, Q shift/interface circuits 151 of type 151 b can be used in the chain to couple the Q configuration outputs of the ASIC 160 to the Q configuration inputs of the FPGA 130 a.

During the normal operation of the IC 110, with reference to FIGS. 1A and 2B, the tester 120 can pull the Test-FPGA signal low (i.e., 0) to cause the Q MUXes 220 of the Q shift/interface circuits 151 of type 151 b to electrically couple the Q configuration outputs of the ASIC 160 to the Q configuration inputs of the FPGA 130 a. In other words, during the normal operation of the IC 110, the shift/interface system 150 is transparent to the FPGA 130 a and the ASIC 160 as far as the configuration data is concerned.

During the structural test 180 (FIG. 1B) of the FPGA 130 a, in step 188, in one embodiment, with the Test-FPGA signal being high, the Q MUXes 220 of the Q shift/interface circuits 151 of type 151 b can apply the Q configuration signal bits from the tester 120 to the Q configuration inputs of the FPGA 130 a which disconnects the Q configuration inputs of the FPGA 130 a from the ASIC 160 during application by the MUXes 220 of the Q configuration signal bits from the tester 120 to the Q configuration inputs of the FPGA 130 a. During the structural test 180 (FIG. 1B), the tester 120 can change the configuration signal bits sent to the FPGA 130 a.

During the testing of the ASIC 160, the tester 120 can pull the Test-FPGA signal low (i.e., 0) to electrically couple the Q outputs of the ASIC 160 to the Q DI inputs of the Q shift/interface circuits 151 of type 151 b. As a result, signals on the Q outputs of the ASIC 160 can be stored in the Q shift/interface circuits 151 of type 151 b and can be later shifted out to the tester 120 for analysis.

In one embodiment, multiple shift/interface circuits 151 of type 151 b can also be used to couple configuration outputs of the ASIC 160 to configuration inputs of the FPGA 130 b in a manner similar to that for the FPGA 130 a. In one embodiment, the testing of the FPGAs 130 a and 130 b can be carried out simultaneously in a similar manner.

FIG. 2C illustrates the shift/interface circuit 151 c (i.e., a shift/interface circuit 151 of type 151 c) that can be used in the shift/interface system 150 of FIG. 1A, in accordance with embodiments of the present invention. With reference to FIGS. 1A and 2C, for type 151 c, in one embodiment, the MUX 220 can have its first and second inputs electrically coupled to an output of the FPGA 130 a (via connection 136 c, a part of connections 133 a of FIG. 1A) and the SO output of the shift/store unit 210, respectively. The MUX 220 can have its output electrically coupled to an input of the ASIC 160 (via connection 155 c, a part of connections 155 of FIG. 1A) and to the DI input of the shift/store unit 210. In one embodiment, the MUX 220 can have its output further electrically coupled directly to the tester 120 via a connection (not shown). As a result, the tester 120 can continuously monitor the output of the FPGA 130 a as long as the MUX 220 selects the output of the FPGA 130 a. The MUX 220 can have its control input receiving a Test-ASIC signal from the tester 120 via connection 157 c, a part of connections 157 of FIG. 1A. In short, the output of the FPGA 130 a is coupled to the input of the ASIC 160 via the shift/interface circuit 151 of type 151 c.

In one embodiment, assume that the FPGA 130 a has R configuration status outputs that need to be directly coupled one-to-one to R configuration status inputs of the ASIC 160 during the normal operation of the IC 110 of FIG. 1A (R is a positive integer). Assume further that the FPGA 130 a has S functional data outputs that need to be electrically coupled one-to-one to S functional data inputs of the ASIC 160 during the normal operation of the IC 110 of FIG. 1A (S is a positive integer). As a result, R shift/interface circuits 151 of type 151 c can be used in the chain to couple the R configuration status outputs of the FPGA 130 a to the R configuration status inputs of the ASIC 160. Also, S shift/interface circuits 151 of type 151 c can be used in the chain to couple the S functional data outputs of the FPGA 130 a to the S functional data inputs of the ASIC 160.

During the normal operation of the IC 110, with reference to FIGS. 1A and 2C, the tester 120 can pull the Test-ASIC signal low (i.e., 0) to cause the R+S MUXes 220 of the R+S shift/interface circuits 151 of type 151 c to electrically couple the R configuration status outputs and S functional data outputs of the FPGA 130 a to the R configuration status inputs and S functional data inputs of the ASIC 160, respectively. In other words, during the normal operation of the IC 110, the shift/interface system 150 is transparent to the FPGA 130 a and the ASIC 160 as far as the FPGA configuration status data and the FPGA functional output data are concerned.

During the structural test 180 (FIG. 1B) of the FPGA 130 a, in step 192, in one embodiment, the tester 120 can pull the Test-ASIC signal low (i.e., 0) to cause the R+S MUXes 220 of the R+S shift/interface circuits 151 of type 151 c to electrically couple the R configuration status outputs and S functional data outputs of the FPGA 130 a to the R+S DI inputs of the R+S shift/store units 210 of the R+S shift/interface circuits 151 of type 151 c. As a result, configuration status data from the FPGA 130 a can be transmitted to and stored in the R shift/interface circuits 151 of type 151 c of the chain and can be later shifted out to the tester 120 for analysis (as part of the second bitstream). Similarly, the FPGA responses at the S functional data outputs of the FPGA 130 a can be transmitted to the S shift/interface circuits 151 of type 151 c of the chain, and the last FPGA response of the FPGA 130 a can be later shifted out to the tester 120 for analysis (as part of the second bitstream).

During the testing of the ASIC 160, the tester 120 can pull the Test-ASIC signal high (i.e., 1) to electrically couple the R+S inputs of the ASIC 160 to the R+S SO outputs of the R+S shift/interface circuits 151 of type 151 c. As a result, ASIC test data can be shifted into the shift/linterface system 150 from the tester 120 (in one embodiment, as part of the first bitstream) and then applied to the R+S inputs of the ASIC 160 via the R+S MUXes 220 of the R+S shift/interface circuits 151 of type 151 c which disconnects the FGPA 130 a from the R+S inputs of the ASIC 160 during application by the MUXes 220 of the ASIC test data to the R+S inputs of the ASIC 160.

In one embodiment, multiple shift/interface circuits 151 of type 151 c can also be used to couple configuration status outputs and functional data outputs of the FPGA 130 b (FIG. 1A) to configuration status inputs and functional data inputs of the ASIC 160, respectively, in a manner similar to that for the FPGA 130 a. In one embodiment, the testing of the FPGAs 130 a and 130 b can be carried out simultaneously in a similar manner.

FIG. 2D illustrates the shift/interface circuit 151 d (i.e., a shift/interface circuit 151 of type 151 d) that can be used in the shift/interface system 150 of FIG. 1A and a MISR stage 142 that can be used in the MISR 140 a of FIG. 1A, in accordance with embodiments of the present invention.

In one embodiment, S MISR stages (not shown) like the MISR stage 142 (or in short, the S MISR stages 142) can be coupled together in daisy chain to form the MISR 140 a of FIG. 1A. In one embodiment, the S MISR stages 142 can be coupled one-to-one to the S functional data outputs (described above) of the FPGA 130 a and also coupled one-to-one to S shift/interface circuits 151 of type 151 d.

In one embodiment, the shift/interface circuit 151 d has a structure similar to the shift/interface circuit 151 c (FIG. 2C), except that in the shift/interface circuit 151 d, the first input of the MUX 220 is coupled to an output of the associated MISR stage 142 (via connection 137) and the output of the MUX 220 is not coupled to the ASIC 160.

During the structural test 180 (FIG. 1B) of the FPGA 130 a, in step 192, in one embodiment, FPGA responses on the S functional data outputs of the FPGA 130 a can be transmitted via connection 136 d to the S associated MISR stages 142 to be processed into the first FPGA response signature. More specifically, when a current FPGA response at the S functional data outputs of the FPGA 130 a is transmitted to the S associated MISR stages 142, the S MISR stages 142 combine the current FPGA response with the previous FPGA response signature to form a current FPGA response signature. At the end, the first FPGA response signature is created at the S outputs of the S MISR stages 142. With the Test-ASIC signal pulled low (i.e., 0) by the tester 120, the S MUXes 220 of the S shift/interface circuits 151 of type 151 d apply the first FPGA response signature from the S MISR stages 142 to the S DI inputs of the S shift/interface circuits 151 of type 151 d. In step 196 (FIG. 1B), the first FPGA response signature is shifted out to the tester 120 for analysis (as part of the second bitstream).

In one embodiment, T more MISR stages 142 (T being a positive integer) can be added to the end of the chain of the S MISR stages 142 so as to reduce the chance of response signature alias. As a result, T more shift/interface circuits 151 of type 151 d corresponding to the T additional MISR stages 142 can be added to the chain. The first FPGA response signature therefore has S+T bits instead of S bits.

In one embodiment, multiple shift/interface circuits 151 of type 151 d and multiple MISR stages 142 can also be coupled to functional data outputs of the FPGA 130 b in a manner similar to that for the FPGA 130 a. In one embodiment, the testing of the FPGAs 130 a and 130 b can be carried out simultaneously in a similar manner with respect to FPGA response signature formation.

FIG. 2E illustrates the shift/interface circuit 151 e (i.e., a shift/interface circuit 151 of type 151 e) that can be used in the shift/interface system 150 of FIG. 1A, in accordance with embodiments of the present invention. With reference to FIGS. 1A and 2E, for type 151 e, in one embodiment, the MUX 220 can have its first and second inputs electrically coupled to an output of the ASIC 160 and an output of the tester 120 (via connection 157 e 2, a part of the connections 157 of FIG. 1A), respectively. The output of the ASIC 160 is also electrically coupled to the DI input of the shift/store unit 220. The MUX 220 can have its output electrically coupled to an input of the FPGA 130 a via connection 136 e. The MUX 220 can have its control input receiving a Test-Enable signal from the tester 120 via connection 157 e 1, a part of connections 157 of FIG. 1A. In one embodiment, the input of the FPGA 130 a can be a stability input of the FPGA 130 a for receiving the stability signal from the tester 120.

During the normal operation of the IC 110, with reference to FIGS. 1A and 2E, the tester 120 can pull the Test-Enable signal low (i.e., 0) to cause the MUX 220 of the shift/interface circuit 151 e to electrically couple the output of the ASIC 160 to the stability input of the FPGA 130 a.

During the structural test 180 (FIG. 1B) of the FPGA 130 a, in steps 182 and 194 in one embodiment, the tester 120 can pull the Test-Enable signal high and also assert the stability signal on the connection 157 e 2. As a result, the asserted stability signal is transmitted to the stability input of the FPGA 130 a via the MUX 220 of the shift/interface circuit 151 e. Therefore, the FPGA 130 a is placed in the stable state. In one embodiment, in step 186 of the structural test 180 (FIG. 1B), the tester 120 can pull the Test-Enable signal high and also deactivate the stability signal on the connection 157 e 2. As a result, the FPGA 130 a is placed in the operation state.

During the testing of the ASIC 160, the shift/store unit 220 can store the bit from the output of the ASIC 160. Later, the stored bit can be shifted out to the tester 120 for analysis.

In one embodiment, another shift/interface circuit 151 of type 151 e can also be used for a stability input of the FPGA 130 b in a manner similar to that for the FPGA 130 a. In one embodiment, the testing of the FPGAs 130 a and 130 b can be carried out simultaneously in a similar manner.

FIG. 3 illustrates one embodiment of the shift/store unit 210 that can be used in the shift/interface circuits 151 a, 151 b, 151 c, 151 d, and 151 e of FIGS. 2A-2E, respectively, in accordance with embodiments of the present invention. In one embodiment, the shift/store unit 210 can comprise latches 310 and 320. The latch 310 can have four inputs I, A, C, and D and one output L1, whereas the latch 320 has two inputs B and E and one output L2.

The inputs SI and DI of the shift/store unit 210 can be electrically coupled to inputs I and D of the latch 310, respectively. The output L1 of the latch 310 is electrically coupled to input E of the latch 320. The output L2 of the latch 320 is electrically coupled to the output SO of the shift/store unit 210. The inputs A, B, and C can be control inputs which can be electrically coupled to the tester 120 via connections 157 (FIG. 1A).

In one embodiment, for the latch 310, if A=1 (i.e., logic high) and C=0 (i.e., logic low), then the output L1 is electrically coupled to input I (i.e., L1=I). If A=0 and C=1, then L1=D. If A=C=0, then L1 remains at its current state. The case A=C=1 is not allowed.

In one embodiment, for the latch 320, if B=1, then L2=E. If B=0, L2 is electrically decoupled from E.

In the embodiments described above, all the shift/interface circuits 151 (FIGS. 2A-2E) of the shift/interface system 150 (FIG. 1A) are coupled together in a single chain. Alternatively, the shift/interface circuits 151 can be coupled together in multiple chains each of which can start from and end at the tester 120. In one embodiment, latches in the ASIC 160 (FIG. 1A) can also be included in the chain(s) of the shift/interface circuits 151.

In the embodiments described above, with reference to FIG. 1A, the FPGAs 130 a and 130 b are shown separate from the ASIC 160. Alternatively, the FPGAs 130 a and 130 b can be embedded in the ASIC 160.

In the embodiments described above, with reference to FIG. 1A, the FPGAs 130 a and 130 b are used for illustration. In general, the present invention is applicable to any macro circuits (not just FPGAs). A macro circuit is itself an integrated circuit (IC). A macro circuit can be integrated in another integrated circuit.

While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention. 

1. A digital system, comprising: (a) N macro circuits, N being a positive integer; (b) an application-specific integrated circuit (ASIC); and (c) a shift/interface system being coupled to the N macro circuits and the ASIC, wherein, in response to the N macro circuits and the ASIC being in normal operation, the shift/interface system is configured to electrically couple each macro circuit of the N macro circuits to the ASIC, wherein, in response to the N macro circuits being tested, the shift/interface system is further configured to electrically disconnect each macro circuit of the N macro circuits from the ASIC, to receive macro circuit test data in series, then to feed the macro circuit test data to the N macro circuits, then to receive macro circuit response data from the N macro circuits, and then to scan-out the macro circuit response data in series, and wherein, in response to the ASIC being tested, the shift/interface system is further configured to electrically disconnect each macro circuit of the N macro circuits from the ASIC, to receive ASIC test data in series, then to feed the ASIC test data to the ASIC, then to receive ASIC response data from the ASIC, and then to scan-out the ASIC response data in series.
 2. The digital system of claim 1, further comprising N multiple-input signature registers (MISRs) electrically coupled one-to-one to the N macro circuits, wherein, in response to the N macro circuits being tested, each i^(th) MISR (i=1,2, . . . , N) of the N MISRs is configured to (i) receive an i^(th) portion of the macro circuit response data from the associated i^(th) macro circuit, (ii) process the i^(th) portion of the macro circuit response data into an i^(th) response signature, and (iii) and feed the i^(th) response signature to the shift/interface system.
 3. The digital system of claim 2, wherein, for i=1,2, . . . , N, the i^(th) MISR comprises K_(i) MISR stages coupled together in a chain and coupled one-to-one to K_(i) output pins of the associated i^(th) macro circuit, K_(i) being a positive integer, wherein the i^(th) MISR further comprises J_(i) MISR stages in a same chain as the K_(i) MISR stages, J_(i) being a non-negative integer, and wherein, for i=1,2, . . . , N, in response to the i^(th) macro circuit being tested, the K_(i) MISR stages are configured to receive the i^(th) portion of the macro circuit response from the K_(i) output pins of the associated i^(th) macro circuit, and the K_(i) MISR stages and the J_(i) MISR stages are configured to process the i^(th) response data into the i^(th) response signature.
 4. The digital system of claim 3, wherein the shift/interface system comprises Σ[K_(i)+J_(i)] (i=1,2, . . . , N) shift/interface circuits, wherein, for i=1,2, . . . , N, the K_(i)+J_(i) shift/interface circuits are coupled together in a chain and coupled one-to-one to the K_(i)+J_(i) MISR stages of the i^(th) MISR, and wherein, for i=1,2, . . . , N, in response to the i^(th) macro circuit being tested, the K_(i)+J_(i) shift/interface circuits are configured to (i) receive the i^(th) response signature from the K_(i)+J_(i) MISR stages of the i^(th) MISR and (ii) then scan-out bits of the i^(th) response signature in series.
 5. The digital system of claim 4, wherein the Σ[K_(i)+J_(i)] (i=1,2, . . . , N) shift/interface circuits are electrically next to each other in a chain.
 6. A system testing and operating method, comprising the steps of: (a) providing a digital system including (i) N macro circuits, (ii) an application-specific integrated circuit (ASIC), and (iii) a shift/interface system being coupled to the N macro circuits and the ASIC; (b) in response to the N macro circuits and the ASIC being in normal operation, using the shift/interface system to electrically couple each macro circuit of the N macro circuits to the ASIC; (c) in response to the N macro circuits being tested, electrically disconnecting each macro circuit of the N macro circuits from the ASIC, (i) scanning-in macro circuit test data in series into the shift/interface system, (ii) feeding the macro circuit test data from the shift/interface system to the N macro circuits, (iii) using the shift/interface system to receive macro circuit response data from the N macro circuits, and (iv) scanning-out the macro circuit response data in series from the shift/interface system; and (d) in response to the ASIC being tested, electrically disconnecting each macro circuit of the N macro circuits from the ASIC, (i) scanning-in ASIC test data in series into the shift/interface system, (ii) feeding the ASIC test data from the shift/interface system to the ASIC, (iii) using the shift/interface system to receive ASIC response data from the ASIC, and (iv) scanning-out the ASIC response data in series from the shift/interface system.
 7. The method of claim 6, wherein N=1.
 8. The method of claim 6, further comprising the steps of: providing, in the digital system, N multiple-input signature registers (MISRs) electrically coupled one-to-one to the N macro circuits, and in response to the N macro circuits being tested, using an i^(th) MISR (i=1,2, . . . , N) of the N MISRs to (i) receive an i^(th) portion of the macro circuit response data from the associated i^(th) macro circuit, (ii) process the i^(th) portion of the macro circuit response data into an i^(th) response signature, and (iii) and feed the i^(th) response signature to the shift/interface system.
 9. The method of claim 8, further comprising the steps of: for i=1,2, . . . , N, providing, in the i^(th) MISR, K_(i) MISR stages and J_(i) MISR stages coupled together in a chain, wherein the K_(i) MISR stages are coupled one-to-one to K_(i) output pins of the associated i^(th) macro circuit, K_(i) being a positive integer and J_(i) being a non-negative integer; for i=1,2, . . . , N, in response to the its macro circuit being tested, (i) using the K_(i) MISR stages to receive the i^(th) portion of the macro circuit response from the K_(i) output pins of the associated i^(th) macro circuit, and then (ii) using the K_(i)+J_(i) MISR stages to process the i^(th) response data into the i^(th) response signature.
 10. The method of claim 9, further comprising the steps of: for i=1,2, . . . , N, providing, in the shift/interface system, K_(i)+J_(i) shift/interface circuits coupled together in a chain and coupled one-to-one to the K_(i)+J_(i) MISR stages of the i^(th) MISR; and for i=1,2, . . . , N, in response to the i^(th) macro circuit being tested, using the K_(i)+J_(i) shift/interface circuits to (i) receive the i^(th) response signature from the K_(i)+J_(i) MISR stages and (ii) then scan-out bits of the i^(th) response signature in series.
 11. The method of claim 10, wherein the Σ(K_(i)+J_(i)), (i=1,2, . . . , N) shift/interface circuits are electrically next to each other in a chain.
 12. A system testing method, comprising the steps of: (a) providing a digital system including (i) a macro circuit, (ii) an application-specific integrated circuit (ASIC), and (iii) a shift/interface system being coupled to the macro circuit and the ASIC, and (iv) a multiple-input signature register (MISR) including K MISR stages, K being a positive integer of at least 2, the K MISR stages being coupled together in a chain, being coupled to K output pins of the macro circuit, and being coupled to K shift/interface circuits of the shift/interface system, wherein the K shift/interface circuits are coupled together in a chain; (b) scanning-in macro circuit test data in series into the shift/interface system; (c) transmitting the macro circuit test data from the shift/interface system to the macro circuit in parallel; (d) using the macro circuit to process the macro circuit test data into macro circuit response data and to present the macro circuit response data at the K output pins of the macro circuit; (e) transmitting the macro circuit response data from the K output pins of the macro circuit to the K MISR stages; (f) using the MISR to process the macro circuit response data into a macro circuit response signature and send the macro circuit response signature to the K shift/interface circuits; and (g) scanning the macro circuit response signature out of the K shift/interface circuits in series.
 13. The method of claim 12, further comprising the steps of: before the step (b) is performed, using the shift/interface system to send a stability signal to the macro circuit so as to place the macro circuit in a safe state; and after the step (c) is performed but before step (d) is performed, using the shift/interface system to (i) send an operation signal to the macro circuit so as to place the macro circuit in an operation state, and (ii) send configuration signals to the macro circuit so as to configure the macro circuit.
 14. The method of claim 12, further comprising the step of, after the step (f) is performed but before step (g) is performed, using the shift/interface system to send the stability signal to the macro circuit so as to place the macro circuit in a safe state.
 15. The method of claim 12, further comprising the step of using a testing circuit to receive the macro circuit response signature from the K shift/interface circuits of the shift/interface system for analysis. 